How to validate array value with form validation

[eluser]Lima[/eluser]
sometime I need pass array from form

Code:

<form name="myform" action="" method="post">
<input type="text" name="group[1]" value="" />
<input type="text" name="group[2]" value="" />
<input type="text" name="group[3]" value="" />
</form>

I got an array

Code:

$group = $this->input->post('group');
// or
$group = $_POST['group'];

How to validate $group with form validation class

Thanks